Strand material is typically collected by winding the strands around a tube carried by a rotating collet. In the case of glass strands, glass filaments are attenuated through bushing tips or orifices at the bottom of heated bushing containing molten glass. The filaments as they are attenuated are coated with a binder and/or size by passing the filaments across the surface of an applicator which is constantly wetted with the binder and/or size to be applied. The filaments are then gathered into a unified strand by a gathering shoe, which is typically a grooved wheel or cylinder. The resulting strand may then be transversed in a vehicle riding in a cam or across the face of a rotating spiral and collected as a forming package on a forming tube carried by a rotating collet.
It is necessary to firmly hold the forming tube onto the face of the collect to avoid slippage of the tube as the collet is rotating. This is necessary, since the rotation of the tube with the forming package thereon provides the attenuative forces for the formation of the filaments. Filament diameter is directly proportional to the tension on the filaments from the rotating collet. Should the forming tube slip, uneven tension will be transmitted to the filaments and thus uneven strand diameter results. This results in unacceptable product.
Several solutions to this problem have been employed by the prior art. A first solution is to form the face of the collet of a plurality of fingers which ride within slots or grooves and which are designed to expand outwardly from the collet due to centrifugal force when the collet is rotated. Thus, the face of a collet itself expands to firmly grasp the forming tube. An example of such a collet can be found in U.S. Pat. No. 3,871,592. While this solution is satisfactory for collets having a large diameter as, for example, 12 inches (30.5 centimeters) or more and rotated at high speeds, such a solution is unsatisfactory for collets of smaller diameter, i.e., in the order of 5 inches (12.7 centimeters) and rotated at slower speeds, as is often the case with larger diameter filaments, since the centrifugal forces necessary to expand the fingers is often insufficient.
A second possible solution which is commonly employed is to form the collet, or portion thereof, of an expandable material and "blow-up" the collet by air pressure. This solution takes two forms. In one form, a bladder or hollow tube of expandable material forms at least a portion of the outer part of the collet and is expanded to firmly grasp the tube placed thereon. Typical of this form are U.S. Pat. Nos. 2,289,453; 2,621,867; 3,139,242; 3,394,902; and 3,834,257.
The other form which this solution may take is to form the collet having an interior tube or bladder which is expanded by air pressure to cause a plurality of protrusions located at the surface of the collet to be forced beyond and protrude from the surface of the collet by the bladder or tube when it is expanded. Typical of this solution are U.S. Pat. Nos. 2,215,069; 3,104,074; and 3,127,124.
A problem common to both forms of the air pressure solutions is that these collets tend to be unevenly balanced when expanded. This results in an eccentric rotation of the collet and the forming package and tube being carried thereon and thus the forming package will produce an uneven tension on the strand and an uneven diameter strand. This effect becomes even more pronounced as the collet speed is increased and thus the collet readily becomes unacceptable for the collection of glass strands.
In U.S. Pat. No. 2,801,858 an expandable collet is disclosed which has a single expandable element which is expanded by compressing it at its ends to expand its diameter as its width is decreased. This is accomplished by manually forcing compaction elements towards each other to compress the expandable element therebetween. This type of collet is evenly balanced when expanded. This solution is useful, however, it requires an operator to manually force the compaction elements together which has been found to be a time-consuming and thus inefficient operation. This method is also employed in U.S. Pat. No. 3,165,279 where the expandable element is extended by forcing a compaction element into it to expand its surfaces outwardly. This, too, requires a manual operation to accomplish the result.
It is desirable, therefore, to produce an expandable collet having the advantages of being evenly balanced to produce a uniform rotation and having the quickness of expansion found in the "blown-up" collets to conserve time in doffing and replacing the forming tube and thus reduce cost and increase efficiency.